Effect of a 2-day very low-energy diet on skeletal muscle insulin sensitivity in obese type 2 diabetic patients on insulin therapy

Early improvement in glycemic control after bariatric surgery and its relationships with insulin, GLP-1, and glucagon secretion in type 2 diabetic patients

BACKGROUND

The surgical treatment of obesity ameliorates metabolic abnormalities in patients with type 2 diabetes. The objective of this study was to evaluate the early effects of Roux-en-Y gastric bypass (RYGB) on metabolic and hormonal parameters in patients with type 2 diabetes (T2DM).

METHODS

Ten patients with T2DM (BMI, 39.7 ± 1.9) were evaluated before and 7, 30, and 90 days after RYGB. A meal test was performed, and plasma insulin, glucose, glucagon, and glucagon-like-peptide 1 (GLP-1) levels were measured at fasting and postprandially.

RESULTS

Seven days after RYGB, a significant reduction was observed in HOMA-IR index from 7.8 ± 5.5 to 2.6 ± 1.7; p < 0.05 was associated with a nonsignificant reduction in body weight. The insulin and GLP-1 curves began to show a peak at 30 min after food ingestion, while there was a progressive decrease in glucagon and blood glucose levels throughout the meal test. Thirty and 90 days after RYGB, along with progressive weight loss, blood glucose and hormonal changes remained in the same direction and became more expressive with the post-meal insulin curve suggesting recovery of the first phase of insulin secretion and with the increase in insulinogenic index, denoting improvement in β-cell function. Furthermore, a positive correlation was found between changes in GLP-1 and insulin levels measured at 30 min after meal (r = 0.6; p = 0.000).

CONCLUSION

Our data suggest that the RYGB surgery, beyond weight loss, induces early beneficial hormonal changes which favor glycemic control in type 2 diabetes.

Early and longer term effects of gastric bypass surgery on tissue-specific insulin sensitivity and beta cell function in morbidly obese patients with and without type 2 diabetes

AIMS/HYPOTHESIS

Bariatric surgery consistently induces remission of type 2 diabetes. We tested whether there are diabetes-specific mechanisms in addition to weight loss.

METHODS

We studied 25 morbidly obese patients (BMI 51.7 ± 1.5 kg/m(2) [mean ± SEM]), 13 with non-insulin-treated type 2 diabetes (HbA(1c) 7.1 ± 0.5% [54 ± 5 mmol/mol]), before and at 2 weeks and 1 year after Roux-en-Y gastric bypass (RYGB). Lean (n = 8, BMI 23.0 ± 0.5 kg/m(2)) and obese (n = 14) volunteers who were BMI-matched (36.0 ± 1.2) to RYGB patients at 1 year after surgery served as controls. We measured insulin-stimulated glucose disposal (M) and substrate utilisation (euglycaemic clamp/indirect calorimetry), endogenous glucose production (EGP) by 6,6-[(2)H(2)]glucose, lipolysis (rate of appearance of [(2)H(5)]glycerol) and beta cell function (acute insulin response to i.v. glucose [AIR] as determined by C-peptide deconvolution).

RESULTS

At baseline, all obese groups showed typical metabolic abnormalities, with M, glucose oxidation and non-oxidative disposal impaired, and EGP, lipolysis, lipid oxidation and energy expenditure increased. Early after RYGB plasma glucose and insulin levels, and energy expenditure had decreased, while lipid oxidation increased, with M, EGP and AIR unchanged. At 1 year post-RYGB (BMI 34.4 ± 1.1 kg/m(2)), all diabetic patients were off glucose-lowering treatment and mean HbA(1c) was 5.4 ± 0.14% (36 ± 2 mmol/mol) (p = 0.03 vs baseline); AIR also improved significantly. In all RYGB patients, M, substrate oxidation, EGP, energy expenditure and lipolysis improved in proportion to weight loss, and were therefore similar to values in obese controls, but still different from those in lean controls.

CONCLUSIONS/INTERPRETATION

In morbidly obese patients, RYGB has metabolic effects on liver, adipose tissue, muscle insulin sensitivity and pattern of substrate utilisation; these effects can be explained by energy intake restriction and weight loss, the former prevailing early after surgery, the latter being dominant in the longer term.

Dietary fat and carbohydrates differentially alter insulin sensitivity during caloric restriction

BACKGROUND & AIMS

We determined the effects of acute and chronic calorie restriction with either a low-fat, high-carbohydrate (HC) diet or a low-carbohydrate (LC) diet on hepatic and skeletal muscle insulin sensitivity.

METHODS

Twenty-two obese subjects (body mass index, 36.5 +/- 0.8 kg/m2) were randomized to an HC (>180 g/day) or LC (<50 g/day) energy-deficit diet. A euglycemic-hyperinsulinemic clamp, muscle biopsy specimens, and magnetic resonance spectroscopy were used to determine insulin action, cellular insulin signaling, and intrahepatic triglyceride (IHTG) content before, after 48 hours, and after approximately 11 weeks (7% weight loss) of diet therapy.

RESULTS

At 48 hours, IHTG content decreased more in the LC than the HC diet group (29.6% +/- 4.8% vs 8.9% +/- 1.4%; P < .05) but was similar in both groups after 7% weight loss (LC diet, 38.0% +/- 4.5%; HC diet, 44.5% +/- 13.5%). Basal glucose production rate decreased more in the LC than the HC diet group at 48 hours (23.4% +/- 2.2% vs 7.2% +/- 1.4%; P < .05) and after 7% weight loss (20.0% +/- 2.4% vs 7.9% +/- 1.2%; P < .05). Insulin-mediated glucose uptake did not change at 48 hours but increased similarly in both groups after 7% weight loss (48.4% +/- 14.3%; P < .05). In both groups, insulin-stimulated phosphorylation of c-Jun-N-terminal kinase decreased by 29% +/- 13% and phosphorylation of Akt and insulin receptor substrate 1 increased by 35% +/- 9% and 36% +/- 9%, respectively, after 7% weight loss (all P < .05).

CONCLUSIONS

Moderate calorie restriction causes temporal changes in liver and skeletal muscle metabolism; 48 hours of calorie restriction affects the liver (IHTG content, hepatic insulin sensitivity, and glucose production), whereas moderate weight loss affects muscle (insulin-mediated glucose uptake and insulin signaling).

Loss of 50% of excess weight using a very low energy diet improves insulin-stimulated glucose disposal and skeletal muscle insulin signalling in obese insulin-treated type 2 diabetic patients

AIMS/HYPOTHESIS

Both energy restriction (ER) per se and weight loss improve glucose metabolism in obese insulin-treated type 2 diabetic patients. Short-term ER decreases basal endogenous glucose production (EGP) but not glucose disposal. In contrast the blood glucose-lowering mechanism of long-term ER with substantial weight loss has not been fully elucidated. The aim of this study was to investigate the effect of loss of 50% of excess weight [50% excess weight reduction (EWR)] on EGP, whole-body insulin sensitivity and the disturbed myocellular insulin-signalling pathway in ten obese insulin-treated type 2 diabetic patients.

METHODS

A euglycaemic-hyperinsulinaemic clamp with stable isotopes ([6,6-(2)H2]glucose and [2H5]glycerol) combined with skeletal muscle biopsies was performed during a very low energy diet (VLED; 1,883 kJ/day) on day 2 and again after 50% EWR. Oral blood glucose-lowering agents and insulin were discontinued 3 weeks prior to the VLED and at the start of the VLED, respectively.

RESULTS

Loss of 50% EWR (20.3+/-2.2 kg from day 2 to day of 50% EWR) normalised basal EGP and improved insulin sensitivity, especially insulin-stimulated glucose disposal (18.8+/-2.0 to 39.1+/-2.8 micromol kg fat-free mass(-1) min(-1), p=0.001). The latter was accompanied by improved insulin signalling at the level of the recently discovered protein kinase B/Akt substrates AS160 and PRAS40 along with a decrease in intramyocellular lipid (IMCL) content.

CONCLUSIONS/INTERPRETATION

Considerable weight loss in obese, insulin-treated type 2 diabetic patients normalises basal EGP and improves insulin sensitivity resulting from an improvement in insulin signal transduction in skeletal muscle. The decrease in IMCL might contribute to this effect.

Insulin-mediated phosphorylation of the proline-rich Akt substrate PRAS40 is impaired in insulin target tissues of high-fat diet-fed rats

Clinical insulin resistance is associated with decreased activation of phosphatidylinositol 3'-kinase (PI3K) and its downstream substrate protein kinase B (PKB)/Akt. However, its physiological protein substrates remain poorly characterized. In the present study, the effect of in vivo insulin action on phosphorylation of the PKB/Akt substrate 40 (PRAS40) was examined. In rat and mice, insulin stimulated PRAS40-Thr246 phosphorylation in skeletal and cardiac muscle, the liver, and adipose tissue in vivo. Physiological hyperinsulinemia increased PRAS40-Thr246 phosphorylation in human skeletal muscle biopsies. In cultured cell lines, insulin-mediated PRAS40 phosphorylation was prevented by the PI3K inhibitors wortmannin and LY294002. Immunohistochemical and immunofluorescence studies showed that phosphorylated PRAS40 is predominantly localized to the nucleus. Finally, in rats fed a high-fat diet (HFD), phosphorylation of PRAS40 was markedly reduced compared with low-fat diet-fed animals in all tissues examined. In conclusion, the current study identifies PRAS40 as a physiological target of in vivo insulin action. Phosphorylation of PRAS40 is increased by insulin in human, rat, and mouse insulin target tissues. In rats, this response is reduced under conditions of HFD-induced insulin resistance.